The work described in this proposal has as its major objectives: (1) the localization of brain photoreceptors which participate in the perception of light cycles which stimulate the growth of the gonads of birds; (2) the localization of brain photoreceptors which participate in the perception of light cycles synchronizing the circadian rhythms of birds; (3) the analysis of functional interrelationships among these photoreceptors and the eyes. Several methods will be employed to produce localized cycles of light and darkness in various areas of the brain and its photosensitivity will be mapped, using as assays the synchronization of the locomotor rhythm, testis growth and circulating levels of LH, as well as a conditioned response to a light pulse. When the photoreceptors have been localized, light will be presented to them individually and in various combinations and their functional relations will be analyzed.